Wave-transformation system of radio broadcast distribution



E. E. CLEMENT v Feb. 25, 1930.

WAVE TRANSFORMATION SYSTEM OF RADIO BROADCAST DISTRIBUTION Filed Feb. 9, 1924 Ill Patented Feb. 25, 1930 UNITED STATES PATENT OFFICE- EDWARD E. CLEMENT, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO EDWARD F. COLLADAY, OF WASHINGTON, DISTRICT OF COLUMBIA WAVE-TRANSFORMATION SYSTEM OF RADIO BROADCAST DISTRIBUTION Application filed February 9, 1924. Serial No. 691,821.

My invention relates to radiophone exchange systems and has for its object to simplify and improve methods of controlling the broadcast distribution of intelligence.

Briefly stated, the invention comprises a radio-wire system, in which two sets of waves are radiated at different frequencies, and both sets are received at each subscribers station, and the combined or resultant potentials are impressed upon the subscribers circuit, whereby electrical variations of a frequency equivalent to the mean between the two primary frequencies, will be produced in the subscribers line to central. At the central'stationvend of the line, a detector, with or without amplifiers, (both radio and audio), receives the radio oscillations, detects and rectifies the same, and returns corresponding audio frequency waves over the line to the subscribers station, where they are rendered intelligible by suitable receiving apparatus, not responsive, to the primary waves. The electrical variations in the line may be amplified by passing through a tube or tubes, that is to say, in one or more stages, at the central station, and sent back over the line thus amplified, to be picked up by the subscriber, and rendered audible at his station in the usual way.

Certain advantages inhere in the arrangement described. One is in respect to the simplicity of line connections, since all radio transmission is through the ether, and the only terminal attachments necessary are multiple taps across the lines, each containing the tuning elements, and one coil of a coupler. At both ends of the line, these are the only elements that need physical attachment thereto, and the tuning is such that audio telephone currents or battery currents are entirely unaflected thereby. Another advantage at the central oflice is the concentration of detector tubes and circuits at central with the battery supply where constant inspection and care are rendered easy and simple.

This system is intended to be used for distant receiving and distribution or for local broadcasting. For distant receiving the central otfice apparatus includes a tuned receiving antenna circuit anda relay-transmitter,-

which sends out the same radio waves amplified; also a local heterodyning transmitter with a properly tuned aerial. The modulations in this case are carried on the relayed waves, and the local heterodyne waves may be unmodulated. Where local broadcasting is desired however, a second modulated local oscillator circuit is provided, which takes the place of the relay transmitter for distant waves. Thus with two local oscillators, it follows that either train of waves may be modulated, and this afi'ords means to give out local programs limited to the subscribers only, without interferin with individual subscribers reception 0 distant stations when practiced with independent apparatus. My invention is illustrated in the accompanying drawing, in which the figure is a diagram showing a central station CS and a subscribers station SS. At the central station are indicated a radio receiving and relaying apparatus RR- and local oscillator L0. The radio relaying apparatus RR has a tuned antenna circuit 1, the local oscillator has a tuned antenna circuit 2. It is quite obvious that interference between these trains of waves can produce no ill effect, since they are intended to heterodyne at the subscribers station and in thesubscribers wired line circuit. At the subscribers station'3 is one antenna circuit tuned to the frequency transmitted by the radio relay RR, and 4 is a similar antenna circuit tuned to the frequency of the central office local oscillator LO. If it be desired to avoid tuning entirely at the subscribers station, it may be done in the following manner: Provide the radio relay set RR with either audio or radio means (such as a primary heterodyne circuit) to change the frequency of the modulated waves received from distant stations over the antenna 1, so that they will always go out locally on a constant wave length. In such case, the local oscillator LO would also be tuned for a constant wave lengtln and it necessarily follows that the'tuning of the subscribers antennae 3 and 4 may then be for constant wave length, as well as any local resonating clrcuit connected therewith.

At the subscribers station I have shown the usual telephone set TS and a jack J bridged across the line to receive a plug P constituting the terminal of a local receiving circuit RC containin the telephone receiverTC and talking con enser AC, the purpose of this being to prevent closing the line for battery current while listening to the relayed and amplified audio current coming from central.

At the central station J J represent the ordinary standard switchboard terminals of any desired type, to which the line 56 is connected for telephone communication with the subscribers station SS. The dotted lines in the middle of the figure represent that portion of the line which extends between the subscribers station and the central ofiice.

' Across the ends, are bridged elements I-I and VCVG, and coupler coils CC and CC. Coupled through coils C and CC is the local circuit 7, containing a detector tube 7 of standard type, the grid circuit of which is adapted to be affected by the electrical variations on the line, and to produce signal currents in the plate circuit, which is inductively connected through the audio transformer AT across the line, thus feedingback audio frequency waves at audio frequency to the subscribers line, where they become intelligible in the receiving instrument TC or its equivalent. It is obvious that any desired number of stages of radio frequency ampli'cation, or audio frequency amplification may be inserted before and after the detector tube 7 and it should also be observed that the lines may be connected through the coupler coils CC to bus circuits and served by tubes 7 or the equivalent, which are common to a plurality of lines. This is possible because all the lines taking the service are receiving the same signals. Neither would this prevent selection of programs, Which is very desirable.

What I claim is:

In a system of radio broadcast distribution, a central station and subscribers stations and wired circuits interconnecting them, means at the central station to relay modulated radio waves received from a distance over the local area, means to transmit heterodyne frequencies therefor over the same area, collector means at the subscribers stations for receiving both the modulated and the heterodyne waves, coupling means to impress said waves simultaneously on the subscribers wires, means at the central ofiice connected to said wires to produce resultant modulated waves due to said modulated and heterodyne waves in the line wires, and to amplify the same, and means at each subscribers station to receive and render audible said amplified waves.

In testimony whereof I hereunto afiix my signature.

EDWARD E. CLEMLEN T. 

